Voted best answer

1

Each serial port can have only one master, but several slaves. The Modbus port configuration on the serial port is for the master only. The slaves are configured in the Program POU using mb_connect function blocks.

Thanks, Its Solved.
I was wondering We have another set of communication where Modbus Master Address is 1 modbus port configuration and is Slave address is 1 in POU and is communicating fine without any issue. But when we have more than one slave, The Master address has to be different from any of the slave !

Even master address 1 and slave address 1 should not really work. I think this is more luck than anything else.

The slave can only respond to requests from the master, the master will not respond to its own requests. So you got lucky that it just happens to work. It's not supposed to. It quite possibly will not work with a different brand of PLC slave.

Answers

0

Please provide a drawing for better understanding.

It is not so clear for me how you build this daisy chain - is that sequent connection between CPU and the 3 slaves?

Usually each COM port in AC800M works as master, but you can connect up to 254 slaves to each com port. So, depends on your cabling, you can connect all the slaves (with different slave addresses) to only one COM port of CI853, in case there are cables point to point (sequence connection).

Other option is the COM3 port in the CPU. It also could be used as a master. So in your configuration you already have 3 COM ports, each could be a master. But I don't see the reason to use separate 3 master-slave lines, in order to connect 3 slaves, if it possible to connect all of them to one master.